It has become common practice to manufacture food patties at a central location for distribution to restaurants, fast-food establishments, grocery stores, and other retail outlets. The most common food patties are hamburger patties molded from ground meat; other food products processed by the same techniques include fish patties, patties formed from flaked or shredded meat, and even patties formed from vegetable foods. The term "food product", as used throughout this specification and the appended claims, refers to any of the various foods identified above and to others having similar properties; the food products processed under the invention are not free-flowing, but are quite viscous and resistant to flow, and are only moderately compressible.
In molding food patties, the food product is usually fed from a hopper or similar container into a food pump which forces the food product, under substantial pressure, through a fill passage extending in a mold cover and then into a plurality of mold cavities in a mold plate. The mold plate is mounted between a base and the mold cover, and is moved in a cyclic rotary or reciprocating motion between a fill position at which it receives food product from the pump and a discharge position at which food patties are discharged from the mold cavities. Effective operation of the molding machine depends upon maintenance of smooth, close, sliding engagement between the mold plate and each of the mold base and the mold cover.
In many food patty molding machines, particularly high volume machines, the pumping pressure for the food product is relatively high. Consequently, the mold cover must be quite strong and rigid in order to achieve sufficient structural integrity to preclude distortion of the mold cover that might cause it to bind against the mold plate. An operating problem is presented if a piece of hard foreign matter passes through the machine; this can scar the surfaces of the mold cover or the mold base that engage the mold plate, with resulting subsequent distortion of the food patties or collection of food product in the scars. If the machine is used to mold patties of varying volume, for efficient operation it may be necessary to change the size of the fill passage in order to produce a well-knit patty, because the molded characteristics of the patty depend to some extent upon the velocity of the food product entering the mold cavities.
In many previously known food patty molding machines, the mold cover has constituted a single, heavy, rigid cover plate. A cover plate of this kind, which may also be an integral part of the food pump, is difficult to remove for cleaning or replacement. Furthermore, a unitary single-plate cover of this kind is usually quite expensive, so that maintenance of a plurality of cover plates adapted to varying mold cavity requirements is economically undesirable.
In the molding machine construction shown in the aforementioned Sandberg et al application, Ser. No. 623,986, the mold cover is of two-part construction, comprising a heavy rigid cover plate upon which is mounted a somewhat thinner auxiliary plate referred to herein as a fill plate, the fill plate being the element of the mold cover immediately adjacent to the mold plate. This construction makes it possible to change the portion of the cover that engages the mold plate without engendering some of the problems noted above. In particular, the mounting arrangement for the fill plate can be one which permits rapid and convenient removal and replacement of that plate, greatly facilitating a changeover from food patties of one size to those of another size. Similarly, a thinner and more readily removable fill plate, as a part of the mold cover, allows for more economical maintenance of the patty molding machine, either by resurfacing of the fill plate or by replacement, to correct for normal wear or for any scarring of the fill plate that might be occasioned by passage of hard foreign material through the machine.
This two-part construction for the mold cover, however, introduces an additional problem. The substantial pressure applied to the food product during the fill portion of the machine cycle is also applied at the point of juncture, in the fill passage, between the fill plate and the cover plate. This pressure tends to force food product between the cover plate and the fill plate; with continuing operation, an excess of food product forced between the two plates tends to deflect the fill plate toward the mold plate, eliminating the normal running clearance for the mold plate and effectively braking the mold plate. This binding or braking action between the mold plate and the fill plate creates a potential overload for the mold plate drive and also produces a marked increase in wear on the fill plate and mold plate surfaces. Both of these effects are highly undesirable and unacceptable in a high volume food patty molding machine.